freqtweak - Realtime audio frequency spectral manipulation

FreqTweak is a tool for FFT-based realtime audio spectral manipulation
and display. It provides several algorithms for processing audio data
in the frequency domain and a highly interactive GUI to manipulate the
associated filters for each. It also provides high-resolution spectral
displays in the form of scrolling-raster spectragrams and energy vs
frequency plots displaying both pre- and post-processed spectra.